1. Field of the Invention
The present invention relates to a variable frequency oscillator system and more particularly to such an oscillator system having a highly stable center frequency output signal with the added flexibility of large excursions about the center frequency.
2. Description of the Prior Art
The prior art has extensively addressed the problem of sychronizing a number of independently operating systems. In the case of communication links, a master timing clock has the slave clocks at remote locations locked to the same frequency for data transmission. In the case of a number of data processing systems communicating with each other or peripheral units, synchronous operation is also desired. There is a known penalty for operating asynchronously which inevitably requires buffer systems that are expensive, and deteriorate system performance.
Synchronous operation, however, requires that the master and slave systems operate at identical frequencies when communicating with each other. Of course, each station must also have its own clock in order to operate independently when not communicating with another unit. All the clocks in the individual units are preferably crystal oscillators as these are the best known for obtaining a stable center frequency. Crystal oscillators have stable center frequencies to an accuracy of 1 cycle/10.sup.7 cycles but their frequency is very difficult to vary about the stable center frequency.
On the other hand, variable frequency oscillators (VFO's) have a widely variable frequency range but lack center frequency stability. The best known VFO's have stability of only 1 cycle/10.sup.5. Moreover, such relatively stable VFO's require very precisely constructed inductors and capacitors and other components usually incompatible with large scale integrated circuit (LSI) construction.